20
Soil acidity
ADDRESSING
BARRIERS TO
LIME USE
By Brian Hughes
SURVEYS BETWEEN 2005 and 2014 of growers in
South Australia with acid soils indicate 40 to 50 per
cent believe liming to be too expensive -- due to lime
sources being too far away and expensive to transport
-- especially in years and areas of low productivity.
While most growers believe that lime benefits
the productivity of acid soils, barriers to lime
use are restricting its application. Of particular
concern is the lack of information available from
lime suppliers on the quality of lime sources and
therefore their effectiveness in lifting soil pH.
Other concerns limiting lime use in SA
include: the availability of machinery to spread
lime; the potential impact of lime application
on the introduction of, or increase in, pests;
and nutritional deficiencies or imbalances.
A new GRDC-funded project running until 2018 will
develop a soil acidity strategy for SA with the goals of
doubling lime sales in SA agricultural areas by 2018 and
lifting grower and adviser capacity in identifying and
treating critical soil pH levels in the surface and subsurface.
The project is extending local pH and trial data
and helping growers and advisers determine the
economics of treating soil acidity through comparing
lime sources and products, trialling precision pH testing
and developing tools for calculating lime rates. □
GRDC Research Code RSS00010
More information: Brian Hughes, Rural Solutions SA,
08 8568 6411, brian.hughes@sa.gov.au
LIME LAGGING
BEHIND ACIDITY
IN VICTORIA
By Lisa Miller
SOUTHERN FARMING SYSTEMS researchers are working with the
Victorian Corangamite Catchment Management Authority (CMA) on three
GRDC-funded soil acidity projects to lift liming use across the region:
¢ soil acidity monitoring within the Corangamite CMA to demonstrate
the soil acidity issue;
¢ trials to measure crop responses to liming in south-west Victoria so
that simple lime-response calculators can be created to help growers
make better liming decisions; and
¢ trials to measure pasture responses to liming and biological amendments
within the Corangamite catchment.
The projects will determine the amount of lime needed in different
soil types to remove production constraints and return soil pH to
optimal levels. This will enable growers to calculate how often to
reapply lime and how much a liming program will cost relative to
the production returns of maintaining a good soil pH profile.
Soil acidity monitoring across the Corangamite catchment indicates there is
an issue with surface soil (0 to 10 centimetres) acidity, with 59 per cent of soil
samples returning pH values below the optimum of 5.0. Thirty-three per cent of
sites had a soil pH lower at 10 to 20cm depth than in the topsoil and strongly
acidic layers (10 to 20cm) existed in 16 per cent of sites in sedimentary,
alluvial and granite soils. In 17 per cent of the paddocks tested soil acidity
issues extended into the subsoil (20 to 30cm). The soils found to be acidic
at depth were mainly formed on sedimentary, alluvial, granite or marl-based
soils and located in high-rainfall areas (600 millimetres plus). Soils formed on
basalt were not acidic at 20 to 30cm as these soils naturally increased in pH
with depth due to their high calcium oxide and magnesium oxide content. □
GRDC Research Code SFS00026
More information: Lisa Miller, Southern Farming Systems, 03 5265 1666,
0488 600 226, lmiller@sfs.org.au
SOURCE: DAFWA
Note: 1.7t/ha of lime with a neutralising value (NV)
of 60 per cent is required to achieve the same pH
change as 1.1t/ha of 90-per-cent NV lime.
FIGURE 1 Amount of lime of
varying neutralising values
required to achieve the same
pH change.
60708090100
Percent neutralising value of lime
Equivalent rates (t/ha)
1.8
1.6
1.4
1.2
1.0
0.8
SOURCE: DAFWA
Note: Coarse and fine limes with the same
neutralising value will treat the same amount of
acidity but the finer lime will do it more quickly.
FIGURE 2 Impact of particle
size on pH change for lime
applied at 2.5t/ha.
0.25 0.50 0.75 1.00
Particle diameter (mm)
Relative efficiency (%)
100
80
60
40
20
0
NEUTRALISING VALUE
AND PARTICLE SIZE
Neutralising value and particle size are the key
indicators of lime quality. Limes with a higher
neutralising value will treat more acidity, while
limes with a greater proportion of fine particles
will increase soil pH more quickly (Figures 1
and 2). With high neutralising limes, less lime
needs to be applied to achieve the same pH
change. The Lime Comparison Calculator
(www.soilquality.org.au/calculators) calculates
and compares the cost-effectiveness of lime
sources. Simply copy and enter the product
specifications of a lime source (neutralising value
and particle size distribution) into the calculator,
along with transport and application costs and
the cost of the lime itself. Information about
neutralising value and particle size distribution
of different agricultural limes are available for
Western Australia from accredited lime suppliers
via The Lime WA Inc (www.limewa.com.au).